1. Field of the Invention
This invention relates to a tape carrier package (TCP) type semiconductor device, and more particularly to a semiconductor device capable of preventing crosstalk which may be caused to easily occur with an increase in the number of pins used and miniaturization and having an excellent high frequency characteristic.
2. Description of the Related Art
Conventionally, the package structure of a semi-conductor device includes a ceramic package used for hermetically sealing a semiconductor device having an integrated circuit formed thereon into a ceramic container formed of alumina, for example, a plastic package obtained by molding a semiconductor chip by use of resin, and a potting resin sealed plastic package used for hermetically sealing a semiconductor chip by mounting the semiconductor chip on a carrier tape and dropping liquid resin on the semiconductor chip.
The carrier tape is also called a TAB (Tape Automated Bonding) tape and a wiring pattern (lead) is formed by laminating a Cu foil, for example, on an insulating film such as a polyimide film and subjecting the Cu foil to the photoetching process. A bump electrode is formed on the semiconductor chip, the wiring pattern formed on the carrier tape is bonded to the bump electrode, then potting resin is dropped on the inner lead portion of the wiring pattern and the semiconductor chip and heat treatment is effected to cure potting resin. Alternatively, the inner lead portion of the wiring pattern and the semiconductor chip are hermetically sealed by use of mold resin instead of the potting resin.
For example, the above TAB technique is disclosed in PROCEEDINGS SECOND INTERNATIONAL TAB SYMPOSIUM FEBRUARY 5-7, 1990 pp. 7-15 "VLSI PACKAGING TRENDS-AN UPDATE" J. Courtney Miller and pp. 230-249 "USING ADVANCED PULSED HOTBAR SOLDER TECHNOLOGY FOR RELIABLE POSITIONING AND MOUNTING OF HIGH LEAD COUNT FLAT PACKS AND TAB DEVICES" Gero Zimmer.
Recently, the number of pins used is increased with an increase in the integration density and the number of functions of the semiconductor device and miniaturization of the semiconductor device, and the width of the lead formed on the carrier tape and the distance between the leads are reduced. Therefore, if adjacent leads are signal lines or power source lines, a magnetic field is generated by currents flowing in the leads according to the corkscrew rule to cause crosstalk. As a result, a current flowing in the signal line or a voltage thereof may be varied and the semiconductor device will be erroneously operated. The crosstalk becomes significant when the operation frequency becomes high (for example, 100 MHz or more).
In order to prevent the crosstalk, there are proposed various methods effected by increasing the distance between the leads, disposing a ground pattern (grounded lead) between the leads and forming a grounded metal film on the under surface (which is opposite to the top surface on which the wiring pattern is formed) of the carrier tape, for example.
However, if the interval between the leads is increased, it becomes difficult to increase the number of pins which can be used in the semiconductor device. Further, if the ground lead is disposed between the leads, it also becomes difficult to increase the number of pins since the ground lead is not used as a signal line which is required by the semiconductor device. In addition, in order to form the grounded metal film on the under surface of the carrier tape, the following steps may be required, for example, to make the carrier tape forming process complex. That is, for example, a metal film is first formed on the under surface of the carrier tape (insulating film) by evaporation. Next, a through hole is formed in the insulating film to permit the metal film to be grounded. After this, the internal portion of the through hole is metal-plated to electrically connect the metal film and the ground lead in the wiring pattern to each other.
Further, a problem that warp or distortion tends to occur in the carrier tape of the TCP type semiconductor device may occur in addition to the crosstalk. If warp or distortion occurs in the carrier tape, the flatness of the outer lead portion is degraded so as to make it difficult to mount the semiconductor element on a printed circuit board by reflow soldering, thereby causing unsatisfactory mounting. The warp or distortion is caused in the carrier tape by the following factors. First, since the carrier tape having a semiconductor chip mounted thereon is wound on a reel and stored and transferred in this state, the carrier tape tends to curl. The warp or distortion in the carrier tape remains in the form of warp or distortion in the TCP itself after the carrier tape is cut into a short sheet in the unit of single semiconductor chip. The curing process of the potting resin is effected with the carrier tape wound on the reel, and since the heat treatment is effected in the curing process, the warp or distortion further occurs in the carrier tape in the heat treatment process.
As a method for preventing the above warp or distortion from occurring in the carrier tape, a method of bonding a reinforcing plate to the carrier tape by use of adhesive agent is disclosed in Japanese Patent Disclosure No. 3-125440. It is also disclosed in the Patent Disclosure that a metal plate can be used as the reinforcing plate, but the structure disclosed in the Patent Disclosure does not have a function as a shielding plate and cannot be used to prevent the above-described crosstalk. Further, with the structure disclosed in the above Patent Disclosure, a space is formed between the leads and the side surface of the lead is exposed so that the moisture resistance will be lowered, thereby permitting the entrance of moisture and making the insulation between the leads insufficient.
Further, the TCP type semiconductor device has a defect that it is difficult to deal with the semiconductor device for storage and transfer in comparison with the other type package structure after it is divided into individual semiconductor devices. The wire bonding type semiconductor device is stored or transferred while it is set on the packing tray having a supporting member for mounting the outer lead on the bottom surface. The reason why the semiconductor device can be supported on the lead portion is that the lead frame is approximately 150 .mu.m in thickness and is the mechanical strength thereof is high. In contrast, the lead of the TCP type semiconductor device is approximately 35 .mu.m and it is impossible to stably support the main body by mounting the outer lead on the supporting member so that it will become difficult to store and transfer the semiconductor device with the semiconductor device set in the packing tray which is used in the prior art.